A touchscreen panel, which is a device for inputting user's commands by touching letters or figures displayed on the screen of an image display device with a human finger or other touch means, is generally attached to an image display device. The touchscreen panel converts the location touched with the human finger, etc. into electrical signals. The electrical signal is used as an input signal.
FIG. 1 is a perspective view illustrating the configuration of a conventional touch detection device.
The touch detection device illustrated in FIG. 1 includes a touch panel 20, a driving device 30 and a circuit substrate 40 connecting them.
The touch panel 20 includes a plurality of sensor pads 22 formed on a substrate 21 and arranged in the form of polygonal matrix, and a plurality of signal wirings connected to the sensor pads 22.
For each signal wiring 23, one end is connected with the sensor pad 22 and the other end extends to the bottom edge of the substrate 21. The sensor pad 22 and signal wiring 23 may be patterned on a cover glass 50.
The driving device 30 selects one by one of the plurality of sensor pads 22 in order, and measures the capacitance of the corresponding sensor pad 22. Accordingly, it detects whether touch is generated.
The signal wiring 23 connects the sensor pad 22 and the driving device 30, and this signal wiring 23 may be patterned with an indium-tin oxide (ITO).
FIG. 2 is a plan view illustrating the configuration of the touch detection device illustrated in FIG. 1.
Referring to FIG. 2, in the touch panel 20, the sensor pads 22 are arranged in a plurality of rows and columns, and the driving device 30 determines the point where the touch is generated based on an output signal from the sensor pads 22. In FIG. 2, the signal wiring 23, which delivers the output signal from each of the sensor pads 22 to the driving device 30, is omitted.
Since the touch generating means forms touch capacitance in a relation with the sensor pad 22, the output signal from the sensor pad 22 where the touch is generated is different from that of the sensor pad where no touch is generated. The touch capacitance may vary depending on the area of the sensor pad 22 with which the touch generating means is in contact. As the area broadens, the touch capacitance increases, and accordingly, the difference in size of signals outputted from the sensor pad 22 before and after touch increases.
When the touch generating means generates touch only on one sensor pad 22, no problem occurs. However, since the sensor pad 22 is formed of a certain size of quadrangle structure and is arranged in rows and columns, a touch generating area may cover a plurality of sensor pads 22.
As an example, as illustrated in FIG. 2, when supposing a case where a touch area T formed by the touch generating means is formed to cover four sensor pads 22_1, 22_2, 22_3 and 22_4, an output signal from each of the four sensor pads 22_1, 22_2, 22_3 and 22_4 is different from that of the sensor pad where no touch is generated.
When supposing that an area contacting the touch generating means is largest in a second sensor pad 22_2, the difference in output signal before and after touch would be the greatest in the second sensor pad 22_2. Thus, the driving device 30 determines that the touch is generated in the second sensor pad 22_2.
A conventional method for detecting touch determines in which sensor pad the touch is generated based on an area contacted by the touch generating means.
As such, when the cross section of the touch generating means is broad and thus the touch generating area T is great, there would be no problem in accuracy. However, when the cross section of the touch generating means is smaller than the area of the sensor pad 22, the following problems may occur.
Supposing that a touch is generated in the area of a fifth sensor pad 22_5 by the touch generating means, the touch may be generated at the upper left side in the area of the fifth sensor pad 22_5 Ta, the touch may be generated around the center Tb, or the touch may be generated at the right side edge Tc. However, since capacitance formed between the touch generating means and the sensor pad 22_5 is the same in all of these three cases, the driving device 30 will determine that the touch is generated in the area of the fifth sensor pad 22_5 in all three cases.
Accordingly, although touch points are different in the three cases, it is determined that the touch is generated in the center, which is a center of the fifth sensor pad 22_5, so an accuracy problem occurs.
Thus, a technology capable of improving accuracy of touch detection, even in minute touch operations, is required. Additionally, it is necessary to detect multiple touch points with improved accuracy.